A microspeaker module is a device for generating vibration of air by an electric signal and reproducing the generated vibration as a sound. As illustrated in FIG. 1, the microspeaker module with a vibration function generally has a shape of rectangular parallelepiped and includes an enclosure 1 serving as a sound box generating sound pressure therein, a microspeaker 2 installed on an upper surface of the enclosure 1 and changing an electrical signal into acoustic pressure to generate vibration of air, and a vibration motor 4 installed within the enclosure 1.
The enclosure 1, a part forming an overall external appearance of the microspeaker module, generally has a shape of a rectangular parallelepiped and has an opening 3 provided on an upper surface thereof to allow the microspeaker 2 to be installed therein.
The vibration module 4 performs a vibration function in response to an electric signal from an electric device.
In case of a general microspeaker module, a magnitude of a back volume of a device in which the microspeaker module is installed significantly affects sound characteristics of the microspeaker module. According to Helmholtz Equation for resonance, a back volume greatly affects equivalent stiffness of air, and thus, as the back volume is smaller, equivalent stiffness is increased to lower sound pressure of a low band and increase a first order resonance frequency.
In particular, in an electric device such as a smartphone or a tablet PC, a microspeaker module takes a small space, considerably reducing a back volume, causing sound pressure to be further lowered in a low band.
In addition, when a vibration motor 4 is installed within the enclosure 1, the back volume is considerably reduced, and as illustrated in FIG. 2, in addition to a signal input unit toward the microspeaker 2, a signal input unit toward the vibration motor 2 needs to be provided, causing a problem in that it is not easy to lead these signal input units to outside when assembling the enclosure 1.